Acetals methoxylation

Benzylidene Acetal Mesitylmethytene Acetal />Methoxyl>enzytklene Acetal... 

Williamson ether synthesis can be hydrolyzed in acid to a compound in which only the acetal methoxyl group at C(l) has been transformed into a hydroxyl group (Fig. 22.41). 

Rhoeadine crystallises from a mixture of chloroform and ether, sublimes at 215-25" /0-02 mm., and then melts at 256-57-5° (vac.), and has [a] / ° -f 232° (CHClj). According to Awe it has m.p. 272-4° (Kofler s micro-apparatus), and [a]] ° -f 243° (CHClj). A crystalline liydriodide, B. HI. 2H2O, was prepared by the addition of potassium iodide to a solution of the alkaloid in acetic acid. Rhoeadine contains one methoxyl group and a dioxymethylene group, but no reactive hydrogen (Zerewitinoff). 

Dicentrine, CgoHjjOjN. (Items 36, 37, 39, 40 list, pp. 172-3.) This alkaloid crystallises, from ether, alcohol, or ethyl acetate in prisms, m.p. 168-9° [a]i) + 62-1° (CHCI3), and yields well-crystallised salts. It contains two methoxyl groups and yields a monoacetyl derivative, colourless leaflets, m.p. 202°, which is not hydrolysed even by boiling alcoholic potash. 1 The methiodide, B. CH3I. HjO, has m.p. 224°, and according to Manske, yields a methine base, m.p. 158-9°, the methiodide of which with potassium hydroxide solution decomposes into trimethylamine and a crystalline substance, presumably a substituted phenanthrenyl-ethylene, which polymerises on recrystallisation. 

Aconitine contains four methoxyl groups and three hydroxyl groups (triacetyl derivative, m.p. 207-8°). On hydrolysis by water under pressure, or by boiling with dilute acid, it loses 1 mol. of acetic acid and forms benzoylaconine, whilst hydrolysis by alkalis eliminates both acetic and benzoic acids and yields aconine. 

Stemonidine, CjoHajOgN. The base has m.p. 116 , [a]jf° — 7 65 , and yields a hydrochloride, m.p. 260 (dec.), and a methiodide, m.p. 248 . It is a tertiary base and of the five oxygen atoms two are in a lactone group and a third is present as methoxyl the functions of the other two are unknown. The alkaloid is unaffected by hydrogen chloride (25 per cent.) in alcohol or acetic acid. The permanganate oxidation products vary with the conditions of the experiment —... 

Many a,/ -unsaturated keto steroids undergo conjugate addition and thereby provide a unique route to aziridines. Treatment of 3j5-hydroxypregna-5, 16-diene-20-one acetate (48) with methoxyl-or ethoxylamine in ethanol under... 

A mixture of 3 -hydroxypregna-5,l6-dien-20-one acetate (10 g), 70 ml of ethanol and 2 ml of methoxylamine is refluxed for 12 hr (Note methoxyl-amine hydrochloride leads to oxime formation). After cooling, another 1.75 ml of methoxylamine is added and the reaction is refluxed for another 12 hr. The solvent is removed in vacuo and the residue is dissolved in ether. Hydrogen chloride gas is passed into the ether solution and the white crystalline salt (113) is filtered off and washed with ether (85% yield crude mp 228-229°). 

The relatively poor resonance activation of the 2-Le-3-aza orientation in bicyclics (cf. Section IV, A) is illustrated by nucleophilic substitutions below. Vigorous conditions are required for methoxylation (110°, 17 hr, quantitative yield) of 3-bromocinnoline and for amination (aqueous ammonia, copper sulfate, 20 hr, high yield) of 3-bromo- (at 130°) or of 3-chloro-derivatives (at 165°). 3,4-Dichlorocinnoline gives predominantly 4-substitution in hydra-zination (90% yield, 20°, 4 days in alcohol), amination (70% yield, 150°, 22 hr in alcohol), and hydroxylation (50% yield, 150°, 22 hr, aqueous ammonia). The poorer-leaving phenoxy group in 3-chloro-4-phenoxycinnoline, is displaced with ammonium acetate (160°, few mins, 60% yield). ... 

The c.d. spectra of these 21 monosaccharides that were studied contain a wealth of information, although proper analysis of the data is not always obvious. However, c.d.-difference spectra between pairs of sugars that differ at only one carbon atom can be used to simplify the analysis. Each of the chromophores in a monosaccharide (hydroxyl, methoxyl, hydroxymethyl, hemiacetal, and acetal) are symmetric and obtain their c.d. by interaction... 

---